The present invention relates generally to the lost pattern process of investment casting, and more specifically to investment casting methods and pattern set-ups that are especially useful for making dental castings and the like.
The invention is particularly concerned with the manufacture of prosthetic dental appliances. A conventional practice of making dental appliances has generally involved the steps of producing a refractory cast of anatomical form duplicating the oral structure of the patient. A wax or plastic pattern of the prosthetic appliance is laid down on the cast and a sprue and gating system is attached to the pattern. The assembly is then covered or invested with refractory material to form a mold. After the mold has dried, the pattern is eliminated, as by heating and melting, and a suitable metal, such as gold or chrome alloy, is introduced into the resulting cavity to form the appliance casting. This general procedure is illustratively described with greater detail in U.S. Pat. Nos. 2,461,416 and 3,192,583.
In carrying out the conventional practice described above, it has been customary to invest a single refractory cast in a mold and to introduce the molten metal into the mold either statically or centrifugally. In the case of static casting operations, the sprue and gating system has been arranged to extend vertically with respect to the pattern and the refractory cast. One explanation for the usual procedure of investing a single cast in a mold is that the casts are relatively heavy and awkward to handle. Because of their shape and weight, it is difficult for an operator to attach several casts to a single support in the manner customarily done with investment casting patterns. Also, the refractory casts may fall off or be knocked from the conventional pattern support members during handling and investing.